1. The problem statement, all variables and given/known data Write out a tree (this will be a big tree) of dependencies and hence write down an expression for ∂z/∂r 2. Relevant equations z=k(x, y)=xy2, x=(w1)(w2)+w3, y=w4; w1=t, w2=t2, w3=2t+1, w4=sin(t); t=r2+2s2 3. The attempt at a solution This is the tree I drew and followed the relevant paths in order to try and write and expression but my expression is to short. I only calculate 2 terms when there is suppose to be 8: http://www.picpaste.com/Untitled_Image-OZCiTMvb.jpg [Broken] This is wrong however. I need 16 leaves at the base. What am I doing wrong?